Dental porcelains



United States Patent @fifice 3,669,773 DENTAL PORCELAINS Jacob A.Saiiir, Los Angeles, Calif., assignor to The Dentists Supply Company ofNew York, York, Pa., a corporation of New York No Drawing. Filed June11, 1959, Ser. No. 819,534

7 Claims. (Cl. 32-8) 'This'invention relates to the art of ceramics indentistry and more particularly to the art of ceramic compositions asused in the manufacture of porcelain dental items such as artificialteeth, crowns, bridge pontics, denture bases, fillings, and other dentalrestorations for which porcelain is desirable.

Porcelain is one of the most important materials used in dentistry. Itlends itself to the manufacturing ofthe most esthetic dentalrestorations since it can be colored to resemble closely the teeth ortissues it must replace.

It has the advantage of excellent chemical qualities since it isinsoluble in the normal fluids of the oral cavity and-in'practically anygiven food or drink likely to pass through the oral cavity. It is alsochemically able to resist the acid or alkali materials frequently usedfor washing artificial tooth members. Also to be considered is the factthat tissues are very tolerant of its presence and remain normal afteryears of contact. I "Porcelain does have, however, one greatdisadvantage. It is quite breakable and repairs are difficult andcostly. Because of the hazard of fragility, its use is curtailed anddentists have resorted to materials generally much less esthetic buthaving greater resistance to fracturing.

It is an object of this invention to strengthen dental porcelains andreduce their frangibility.

lt is another object of this invention to improve the esthetics ofporcelain artificial teeth and denttires.-

Still another object of this invention is to attain artificial teeth anddentures with greater resistance to checking or cracking withinsubstantial temperature ranges.

A further object of this invention'is to' achieve artificial teeth withgreater impact strength and hence greater resistance to chipping. v

Other objects, advantages, and-features of the invention will becomeapparent from the following disclosure, which is intended to beillustrative and not limitative in scope.

This invention comprises the-use of highly refractory glass fibersintermixed with the ceramic compositions now employed for the making ofvarious porcelain items for dental use.

2 i instead to part from one another when the binder and moisture areremoved and each particle is left to expand or contract to its owncoefiicient;

It has been noted that, when placed into a kiln for burning, ceramiccompositions for making poreclain crack? into many piecesbetween'thetemperatures of'700',F. and 1100 F., after. which, when-muchhighertempera. tures are reached, they begin to fuse and coalesceto'form,

a mass thatis more or less a solid but which: is shownto have trappedwithin it a considerable number of air bubbles. I t i,

Due to:the high viscosity of molten porcelain even the high vacuums usedin furnacesduring; the fusing. period generally-serves to remove bubblesonly from the surface, leaving the porcelain in-the interior, generallywith imperfect coalescence and full of minute air. spaces.

The prior art practice has been predicated on the concept of utilizingvery finely milled powders, preferably milled to a particle size to passa 170 mesh sieve. To this powdered porcelain is added water and a binderfor the purpose of producing a mass that is plastic which can be shapedto whatever form is needed.

The binder is generally starch, sugar, deXtrin, gum tragacanth, or anyother material capable of holding the powdered porcelain together duringthe manipulation and disposable by burning in the furnace where theporcelain item is placed for fusing.

It can be seen that the evaporation and burning of the binder will leavespaces, small though they may be, between the particles of porcelainthat it was their duty to hold together during the molding period.

Porcelain is generally composed of several materials such as frittedground feldspar, magnesium silicate, kaolin, boric oxide and variousother ingredients, depending on the type of porcelain desired. It can beseen that the coefiicient of expansion in each of these materials mayvary to a smaller or greater degree so that there is a tendency fordiffering particles not to adhere to each other but In accordance withthe present invention is=has been found that the additionof from-5%rto67%-'ofhighly. refractory glass fibers todental porcelain-compositionsgreatly increases the physical. strength .of the end-dental; product jIndicative of-an expedient procedure-aforobtaining highly refractoryglass fibers is that. diSCIOSBd bYh-fll5, patents to -John:C.- McMullen,No.-- ;.2 ,873,19 7-.- ,and.N0; 2,557,834. In accordance with thesedisclosures. ahighly.

F. can be made-by fusing-the following- Smu Alumina- 201 45, Zirconiato;2Q

with the silicato alumina weight ratio of at least 4 If desired, theabove described compositions'may contain, in additionto' parts by'total' wei'g'ht' of silica, alumina and zirc on'ia, up to aboutsix'parts by'weight of a modifying agent s'uch'as b o'rax glass, withoutapparent detrimental effect on the physical natnrethere of; An exampleofthe procedure from. the'raw batch to-j'the final fiber'is given inPatent No; 2,873,197. The following composition bywe'ight was prepared 7grade white alumina ore j White sand- 49.75 Zircon v3.7

' The above composition, thoroughlymixed, was fused in an arc furnace ofthe type commonlyused for making alumina abrasive materials until asubstantial bath {of molten "material was obtained; f 'The'-"furnace[then tilted to allow the molten-material to pour "from the-fut nace inthe form of a small stream" that irl'ipinged'on'the periphery of one ofthe tw'o't welve inchrotors that'were rotating'at about 4200 rpm; Theaxeso-f theftworotors were substantially parallel with'-' about al threeinchspace between their 'motors'peripheriesi" The stream of moltenmaterial was dissipated in the 'formof fine fibrous mate rial," andthefollowing was given-as a typical chemical analysisof theresultingfibrou's materiah' .'Pe1CBl'lt Alumina 42.75 Silica 52.25

Zirconia" I 5.00

- Patented Dec. 25, 19.62 V

' or dentures will be more nearly as they were sculptured,

making for results that are more true and hence more esthetic.

The use of highly refractory glass fibers makes possible a reduction inthe amount of binder required other than water and in many instancesentirely substitutes for the binder. Since it is the burning out of thebinder that leaves the voids and bubbles so undesirable in finisheddental porcelain items, it can be seen that by using glass fibers a muchdenser porcelain is obtained.

If desired, these highly refractory glass fibers may-be given a thincoating of some substance suitable for strengthening the fiber and thiscoating may be combustible or not combustible at porcelain fusingtemperatures. Recommended are starch, phenol formaldehyde, glycoldimethacrylate polyamide, butyl methacrylate, polyvinol butyl, polyvinolacetal and polyvinol formal and combinations thereof, any other coatingwhich will strengthen the fibers through the period of the manipulationof the porcelain composition.

It is preferable that this coating be qutie thin and consist of onlyabout .()2% by weight of the fiber itself. Also, where a protective coaton fibers is desirable, it must be allowed to dry before cutting intoshort lengths is attempted. Cutting may be accomplished by any expedientthat severs the fibers or by hammermilling.

Since these highly refractory fibers are added as an inert filler to theceramic porcelain composition, their full value as an ever presentreinforcing agent and framework is best obtained when fibers used have afusing point of at least one or two hundred degrees above the fusingpoint of the fusible ceramic used.

Also, since the addition of glass fibers may impart a slight degree ofopacity, it is understood that their use will be selective. In thebaking of a tooth structure, for example, the fibers will be addedperhaps only to the dentin portion, but their presence will impartstrength and durability to the entire tooth. Similarly, by adding fibersto portions of a denture, denture base, or any prosthetic appliancewhere slight opacity is not a drawback, not only those areas but theentire restoration will be better suited to long wearing.

The use of these highly refractory glass fibers makes possible anotherway to increase the esthetic results ofthe porcelain compositions towhich they are added. Coloring matter can be incorporated. This meansthat now can be simulated the thousands of small capillaries in tissues,the enamel rods in natural enamel, blood vessels, or any naturalcontrast or occurrence in structure or tissue that it would be an assetto duplicate.

It is understood that dyes for this purpose must withstand hightemperatures, must be inorganic, and should preferably be added, inminute amounts, to the original formula given earlier for the making ofthe highly refractory glass fiber itself. To obtain a good gum color,for example, cadmium selenide red is suggested. A variation in amountused will give pinks. Titanium oxide is satisfactory for light browns,antimony pentoxide and yellow chromium oxide for browns. Glass fibers ofvarious colors and differing shades may be desirable in the same dentalprosthesis for a better final effect. Then, too, glass fibers of morethan one color can be used at the same time While the invention has beendescribed in accordance with desirable embodiments and details ofprocedure, it i: obvious that many changes and modifications may br madein the details thereof and in the characteristics 0. the compositionsand articles obtained therefrom withou departing from the spirit of theinvention as defined in th following claims.

I claim:

1. A composition for the fabricating of various porcelaii dentalprosthetic appliances, comprising a porcelainou material and at least 5%by weight of highly refractor glass fibers, said fibers having a fusingpoint higher tha1 the point of vitrification of said porcelainousmaterial 2. A composition adapted for the fabricating of variouvitrified porcelain dental prosthetic appliances, comprisin avitrifiable porcelainous material and at least 5% b weight of an amountof highly refractory glass fibers, sai fibers precoated with a thinlayer of a plastic materia said highly refractory fibers having a fusingpoint highe than the point at which said porcelainous material vitrific:

3. A ceramic composition adapted for dental prosthes containing aporcelainous material and tinted, highly It fractory glass fiber inproportion by weight of fro1 S to 67% said highly refractory glass fiberhaving a fusin point higher than the point of vitrification of saidporcr lainous material.

4. An artificial porcelain tooth comprising a body dentin portion and acovering or enamel portion, high] refractory glass fibers incorporatedin said body portio tinted to simulate the dentin portion as found in anatur: tooth and highly refractory glass fibers incorporated i saidcovering portion tinted to simulate enamel as foun in a natural tooth,said highly refractory glass fibers ha ing a fusing point higher thanthe temperature at whic the porcelain from which the enamel and bodyportion at formed is fired to vitrify it.

5. An artificial dental appliance comprised of a vitrific dental ceramiccomposition, some portions of said art ficial appliance havingincorporated therein inert gla fibers of more highly refractory naturethan said ceram composition.

6. An artificial dental appliance comprised of a vitrifi dental ceramiccomposition into which is incorporatr highly refractory glass fibershaving a fusing point high than the temperature at which the ceramiccompositit vitrifies to form an inert network for strengthening sadental appliance.

7. A dental ceramic material of which to form vitrifir porcelain teethsaid material comprising pulverized u fired porcelain material andrefractory glass fibers havii a melting point higher than thetemperature of vitrific tion of said porcelain material intimatelyadmixed ther with, said glass fibers having a thin coating thereon ofmaterial suitable for strengthening the fiber during mani ulation of thematerial.

References Cited in the file of this patent UNITED STATES PATENTS

1. A COMPOSITION FOR THE FABRICATING OF VARIOUS PORCELAIN DENTALPROSTHETIC APPLIANCES, COMPRISING A PORCELAINOUS MATERIAL AND AT LEAST5% BY WEIGHT OF HIGHLY REFRACTORY GLASS FIBERS, SAID FIBERS HAVING AFUSING POINT HIGHER THAN THE POINT OF VITRIFICATION OF SAID PORCELAINOUSMATERIAL.